Cyclohexanol and cyclohexanone can be prepared by catalytic hydrogenation of phenol and by other methods such as cleavage of cyclohexylbenzene. In general, hydrogenation of phenol is incomplete and it is necessary to separate unreacted phenol from the products. Further in the oxidation of cyclohexylbenzene, phenol and cyclohexanone are formed as reaction products and must be separated. Cyclohexanol and cyclohexanone both form azeotropes with phenol making their complete recovery by fractional distillation impossible.
E. Field in U.S. Pat. No. 2,265,939, issued Dec. 9, 1941, discloses that compounds containing two alcoholic hydroxy groups such as glycol can be employed for separating phenol from cyclohexanol and/or cyclohexanone.
H. M. Walker in U.S. Pat. No. 2,762,760, issued Sept. 11, 1956, discloses extractive distillation of phenol-containing mixtures of cyclohexanone or cyclohexanol with water.
G. B. Frozzard et al. in U.S. Pat. No. 4,016,049, issued Apr. 5, 1977, disclose separation of phenol/cyclohexanone azeotrope by extractive distillation with an adipic acid diester.
Murtha et al. in U.S. Pat. Nos. 4,115,204; 4,115,205; 4,115,206; and 4,115,207 issued Sept. 19, 1978, disclose phenol-, cyclohexanone-, and cyclohexylbenzene-containing mixtures are extractively distilled to provide overhead of cyclohexanone and a kettle product substantially free of cyclohexanone by employing an N,N-disubstituted amide; an N-substituted lactam, an organic carbonate or a trisubstituted phosphate extractive agent.